1. Field of the Invention
The present invention relates to a method and a device for processing a substrate which are used in photolithography for forming a predetermined circuit pattern on a substrate for a semiconductor wafer or a liquid crystal display (LCD).
2. Description of the Related Art
The substrate processing device is disclosed in, for example, U.S. Pat. No. 6,444,029B1. Operations of a main carrying mechanism and a semiconductor wafer in the conventional device will be described by referring to FIG. 1. Two main carrying mechanisms 15A, 15B cooperatively carry a wafer W in a sequence of a cassette stage 11→a TRS1→a CPL1→a coating unit (COT)→a TRS2→an LHP1→a CPL2→an interface section 1B on an approach route. Then, the main carrying mechanisms 15A, 15B turn around to change directions, and cooperatively carry the wafer W in a sequence of the interface section 1B→a PEB→a CPL3→a developing unit (DEV)→an LHP2→a TRS3→a TRS4→the cassette stage 11 on a return route. The TRS1, TRS4 are transfer units to transfer the wafer between an auxiliary carrying mechanism (not shown) and the main carrying mechanism 15A. The TRS2, TRS3 are transfer units to transfer the wafer between the main carrying mechanisms 15A, 15B.
One main carrying mechanism 15A moves along a cyclic route of the TRS1→the CPL1→the coating unit (COT)→the TRS2→the TRS3→the TRS4→the TRS1 in a processing section 1A. One round of the main carrying mechanism 15A along this cyclic route is called “one cycle movement of the main carrying mechanism 15A”. The other main carrying mechanism 15B moves along a cyclic route of the TRS2→the LHP1→the CPL2→the PEB→the CPL3→the developing unit (DEV)→the LHP2→the TRS3→the TRS2 in the processing section 1A. One round of the main carrying mechanism 15B along this cyclic route is called “one cycle movement of the main carrying mechanism 15B”. Operations of the main carrying mechanisms 15A, 15B during the cycle movements are controlled by a predetermined program of a control section, and forward movements and stopping are repeated without any backtracking on the cyclic routes.
Each of the main carrying mechanisms 15A, 15B comprises two upper and lower arms to load/unload the wafer W on a processing unit. For example, the main carrying mechanism 15A receives an n-th wafer Wn from the TRS1, and carries it to the CPL1 of a next step. Then, the mechanism 15A makes one cycle movement along the cyclic route, and returns to the TRS1 to receive a next (n+1)-th wafer W(n+1) therefrom.
Thus, for each one cycle movement of the main carrying mechanism 15A, wafers W are carried one by one from the cassette section 11 into the processing section 1A through the TRS1. Further, for each one cycle movement of the main carrying mechanism 15A, the wafers W are carried one by one from the processing section 1A out to the cassette section 11 through the TRS4.
On the other hand, for each one cycle movement of the main carried mechanism 15B, the wafers W are transferred one by one to the interface section 1B through the CPL1. Further, for each one cycle movement of the main carrying mechanism 15B, the wafers W are received one by one from the interface unit 1B through the PEB unit. By sequentially repeating these operations, a predetermined process is carried out for all the wafers of lots.
For example, at the coating unit (COT), a resist is spin-coated on the wafer W. At this time, a resist solution in a tank is fed by pressure through a pump to a supply line, and then supplied through the supply line into a nozzle. Here, if supply of the resist solution to the wafer W is stopped, the resist solution stays in the nozzle or the supply line for a long time, which changes the properties (mainly, the solvent volatilizes, which changes the resist viscosity). Thus, between a preceding lot and a succeeding lot, i.e., while the resist is not coated on the wafer W, a so-called dummy dispense is carried out to discharge the staying resist solution from the nozzle or the supply line. This dummy dispense is similarly carried out in the developing unit (DEV).
As described above, the main carrying mechanisms 15A, 15B only move forward or stop without backtracking on the cyclic routes. In this case, if the dummy dispense is carried out at the coating unit (COT), the main carrying mechanism 15A stops at the coating unit (COT) to be set on standby until the dummy dispense is finished. Similarly, if the dummy dispense is carried out at the developing unit (DEV), the other main carrying mechanism 15B stops at the developing unit (DEV) to be set on standby.
Now, explanation is made by taking an example of carrying out the dummy dispense at the coating unit (COT) between a preceding lot A (1 lot: 25 wafers) and a succeeding lot B. When resist coating is finished on a last wafer A25 of the preceding lot A, the main carrying mechanism 15A takes out a head wafer B01 of the succeeding lot B from the CPL1 of a previous step by one arm, and the wafer A25 from the coating unit (COT) by the other arm.
On the other hand, there is a wafer A24 of the preceding lot A in the TRS2 of a next step of the coating unit (COT). This wafer A24 is carried to the LHP1 of a next step by the other main carrying mechanism 15B. Accordingly, after the wafer A24 is taken out from the TRS2, the main carrying mechanism 15A transfers the wafer A25 to the TRS2 by the other arm.
Subsequently, one arm of the main carrying mechanism 15A transfers the wafer B01 to the coating unit. However, if the dummy dispense is carried out at the coating unit (COT), since the wafer B01 cannot be carried into the coating unit (COT), the main carrying mechanism 15A is set on standby while holding the wafer B01. Therefore, carrying of the wafer B01 by the main carrying mechanism 15A stops.
Even if the main carrying mechanism 15A carries the wafer B01 into the coating unit (COT) before the dummy dispense, finally the main carrying mechanism 15A stops during the execution of the dummy dispense or the coating of the resist solution on the wafer B01. Thus, the stopping time of the main carrying mechanism 15A becomes longer by an amount necessary for the dummy dispense at the coating unit (COT). The same occurs in the main carrying mechanism 15B when the dummy dispense is carried out at the developing unit (DEV). On the whole, therefore, transfer of the wafer W is not smooth between the main carrying mechanisms 15A, 15B in the processing section 1A, which impedes improvement of throughput.